So happy to see that Obsidian has a thriving plugin ecosystem. Been considering creating an Obsidian plugin as an excuse to learn typescript, but every time I wonder whether a plugin for $foo exists, the answer turns out to be yes.
Simple idea: mark entire notes or portions of notes as “deprecated” and then have a toggle button that shows/hides deprecated text.
I note that obsidian itself is free. I pay for the built-in sync as that's cheaper than implementing it myself, and there are other paths to sending the developers money, but they're all optional.